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Help! => Hints, Tips & Tricks => Topic started by: Gas_mantle on December 19, 2017, 03:13:19 AM

Title: Video - a skilled machinist shows how to turn small diameters
Post by: Gas_mantle on December 19, 2017, 03:13:19 AM
The title says it all.

I came across the video by accident and thought the technique he uses to turn steel from 1/2" to 30 thou dia in one pass may be of interest.

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Title: Re: Video - a skilled machinist shows how to turn small diameters
Post by: 90LX_Notch on December 19, 2017, 09:15:22 AM
Joe "Pie" in my opinion has the best machining content videos on YouTube. 

-Bob
Title: Re: Video - a skilled machinist shows how to turn small diameters
Post by: simplyloco on December 19, 2017, 11:33:58 AM
Interesting stuff, which any competent machinist should be capable of, but I would look in my SS drawer first and find some 30 thou wire .....  :lolb:
Title: Re: Video - a skilled machinist shows how to turn small diameters
Post by: kvom on December 19, 2017, 01:00:41 PM
I wonder what HP the lathe needs for that cut.
Title: Re: Video - a skilled machinist shows how to turn small diameters
Post by: Jasonb on December 19, 2017, 02:00:47 PM
Does not need to be massively powerful really it is no bigger a cut than drilling a 1/2" hole. My far eastern 11x28 will take off a 0.250 depth of cut in steel if I want it to that's 1/2" off dia, would no doubt be a bit more effort in stainless though as this is on 1" bar would probably equal things out.

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Title: Re: Video - a skilled machinist shows how to turn small diameters
Post by: simplyloco on December 19, 2017, 05:04:52 PM
I wonder what HP the lathe needs for that cut.

IIRC the man said he was using a 3 to 4 thou feed: this slow rate with a sharp new tool means that even a little lathe made of compressed rice paper would cope!  :mischief:
Title: Re: Video - a skilled machinist shows how to turn small diameters
Post by: Vixen on December 19, 2017, 05:52:34 PM
Explain?? :facepalm:
Title: Re: Video - a skilled machinist shows how to turn small diameters
Post by: kvom on December 20, 2017, 01:07:31 AM
Not so slow.  1200 rpm *.004/rev = 4.8 inches/minute
Title: Re: Video - a skilled machinist shows how to turn small diameters
Post by: Jasonb on December 20, 2017, 07:39:27 AM
Kvom, It can be called a" slow" rate irrispective of spindle speed as whatever the spindle is running at the tool will still advance the same amount per rev. Feed rate is not the distance moved per minute, it is distance /rev. Though I would have said 4thou /rev was a medium/high feed on a hobby lathe.

Interesting thing is that he is not cutting at anything like 0.004" per rev, take another look at the video and it takes him about 30secs to do that first cut which is about the dia of the bar so that is 0.5" per min which means he probably meant to say 0.0004" feed. That video of mine is cutting at my slowest feed of 0.0025" /rev. Wonder how many people have tried doing what he shows at 0.004" and had a big jam up! As they say don't believe all you see on you-tube :ShakeHead:

Mike, if it was Dave's comment you wanted explained than the rule of thumb is that you can remove 1 cu in of metal per minute for each 1HP that you have. So if you only hay an 1/8" HP motor then set the feed rate fine enough so that you are removing less than 0.125cu in of material and your small motored lathe should cope. Don't quite agree with dave's bit about rice paper as you would still want a ridgid machine to do it.

EDIT my feed rate changed.
Title: Re: Video - a skilled machinist shows how to turn small diameters
Post by: Jo on December 20, 2017, 08:18:41 AM
.....whatever the spindle is running at the tool will still advance the same amount per rev.

Only true for lathes which gear their surfacing fed from the headstock ::)

Jo
Title: Re: Video - a skilled machinist shows how to turn small diameters
Post by: Jasonb on December 20, 2017, 09:13:33 AM
I know what you are saying Jo but for a feed rate of 0.004" per rev even with your variable speed feed you would still need to reset the speed of the carage to suit a change of the spindle speed if you were to maintain the quoted 0.004" cut per rev. Any change in your spindle speed and you would no longer be cutting at 0.004"

You are also talking about distance moved/time not the usual way feed rate is expressed as distance moved/rev
Title: Re: Video - a skilled machinist shows how to turn small diameters
Post by: Vixen on December 20, 2017, 09:31:43 AM
Don't quite agree with dave's bit about rice paper as you would still want a ridgid machine to do it.

That's the bit I wanted Dave to explain. I would not attempt to repeat this trick on anything less than a big, rigid and 'tight' lathe.

Mike
Title: Re: Video - a skilled machinist shows how to turn small diameters
Post by: Graham Meek on December 20, 2017, 12:36:56 PM
I well remember visiting the Hardinge stand at one of the Metalworking Exhibitions and seeing 1" Mild Steel being turned down to 0.0625". The cut was taken in one pass. The diameter produced was smooth, spot on size and free from any imperfections. The tool used was a HSS knife tool. While it was a very good party piece the wastage of material just to get some 0.0625" rod is not something I would like to do.

I favour a more systematic approach, the attached photographs give my solution to turning long slender shafts, but with out the wastage. The smallest diameter I have done so far is 0.051 for some 12 BA studs. The maximum turned length is dependent on the stiffness of the original bar stock. The longest 3/32 diameter I have turned in one pass is 3", but I feel this set-up could be used to produce longer turned bar. I have just not had the requirement.

The maximum diameter stock that this attachment will deal with is 10 mm. (I apologise for the mixed measuring systems).

My best regards
Gray,
Title: Re: Video - a skilled machinist shows how to turn small diameters
Post by: Bjorn_B on December 20, 2017, 04:09:26 PM
Wish you had not shown that tool Gray.. Now I must make one :)  :happyreader:
Title: Re: Video - a skilled machinist shows how to turn small diameters
Post by: petertha on December 20, 2017, 05:19:23 PM
What a brilliant tool, I want to make one! Hopefully understand correctly: The V block is positioned & secured to rub/support the larger stock diameter. Is the purpose of the Delrin washered bolt (green arrow) to allow the cutter to advance with enough friction just by turning the set screw (red arrow)? Under cutting load, the HSS bit cannot back out because of the set screw & it cant rotate out of position because of the washer/bolt & held captive in the slot?

The little pop marks around the set screw I assume are depth graduation reference? What size is the set screw for reference?

I've seen a similar principle used to turn long skinny shafts (but not as compact or elegant). In that case I guess you would have to re-adjust the V slider position to the new diameter each pass? Is the tool intended to be used in this manner too, or it mostly for turning down relatively short sections?
Title: Re: Video - a skilled machinist shows how to turn small diameters
Post by: Roger B on December 20, 2017, 05:28:07 PM
Wish you had not shown that tool Gray.. Now I must make one :)  :happyreader:

+1  :wine1:
Title: Re: Video - a skilled machinist shows how to turn small diameters
Post by: Graham Meek on December 20, 2017, 05:54:47 PM
The semicircular pad beneath the tool bit is the clamping medium. In the view attached the clamping grubscrew can be seen next to the location slot . The hole through the Boring tool holder and through the Box Turning tool means there is no restriction on the length that can be turned. The restriction is the rigidity of the parent barstock sticking out of the chuck jaws. The material in the photos is 4 mm (5/32) mild steel. This will easily support itself with up to 100 mm (4") sticking out of the jaws.

The tool is designed to reduce the stock in one pass. Coarse adjustments on the tool are carried out by the M3 grubscrew pressing on the back of the tool bit. One full turn reduces the bar stock by 1 mm, (0.5 mm Pitch). Fine adjustment is carried out via the slotted screw. This works on the differential screw principle. The thread in the slotted plate is M5 x 0.8 P, the extreme end of the adjustment screw is threaded M4 x 0.75 P. The M4 thread screws into the main body of the tool. One complete turn of the slotted screw moves the tool 0.05 mm which reduces the bar by 0.1 mm.  Moving from one dot to the next, (10 dots), means the diameter is reduced by 0.01 mm.

The fine adjustment was an add on. I had originally tried setting the tool by turning down the end of the bar first and urging the tool bit against the turned down portion. Hit and miss would describe the outcome. More miss I hasten to add. Adding the fine adjustment means the tool can be set very quickly and be right first time.

My best regards
Gray,